The present invention relates to a process for preparing olefinically unsaturated carbonyl compounds by oxidative dehydrogenation of alcohols in an oxygenous atmosphere over a supported catalyst.
The oxidative dehydrogenation of unsaturated alcohols to aldehydes is known per se and is described in the literature.
DE-A-25 17 859 describes the dehydrogenation of unsaturated alcohols over copper catalysts, which is performed essentially in the absence of oxygen. This forms mixtures of different aldehydes which have to be separated into the components thereof in complex separating operations if pure products are desired.
DE-B 20 20 865 and DE-B-20 41 976 describe the dehydrogenation of β,γ-unsaturated alcohols or α,β-unsaturated alcohols to α,β-unsaturated aldehydes at temperatures in the range from 150 to 600° C. The dehydrogenation catalysts mentioned include mixed catalysts, for example those composed of copper and silver. A disadvantage is that considerable amounts of nucleophilic substances have to be added.
U.S. Pat. No. 4,154,762 describes a process for preparing aldehydes and ketones, by which the corresponding alcohols are converted at temperatures in the range from 250 to 600° C. in the presence of a gold catalyst. This process uses a solid gold catalyst, which is therefore correspondingly expensive.
EP-A-244 632 describes a tube bundle reactor for performance of catalytic organic reactions in the gas phase, which is characterized by particular dimensions of the reaction tube lengths relative to the internal diameter. The oxidative dehydrogenation is performed at temperatures in the range from 300 to 600° C. over a supported catalyst.
EP-A-881 206 describes a process for continuous industrial preparation of unsaturated aliphatic aldehydes in a tube bundle reactor, in which the actual reaction is preceded by passing the reaction mixture through the supported catalyst above the dew point of the alcohol used but below the start temperature of the reaction. The actual oxidative dehydrogenation in the process described in this document also takes place at temperatures of 300° C. or more.
Angew. Chem. Int. Ed. 2007, 47, pages 138-141 describes oxidizing agent-free alcohol dehydrogenation using a recyclable supported silver catalyst on a hydrotalcite support. The reaction is performed in the absence of oxygen, for is example in an argon atmosphere. According to example 16 in Tab. 1, an olefinically unsaturated alcohol with a phenyl substituent is converted to the corresponding aldehyde in the absence of oxygen.